1. Field of the Invention
The present invention relates to a polishing composition, a polishing process of a substrate to be polished by applying the polishing composition; and a process for producing a substrate by applying the polishing composition.
2. Discussion of the Related Art
With the increase in the magnetic recording density in the recent years, a floating amount of the magnetic head in memory magnetic disk drive for read-write of magnetic information has been becoming increasingly low. As a result, in the step of surface-polishing in a process of producing a magnetic disk substrate, it has been required to produce a high-precision disk surface capable of having a small floating amount of a magnetic head, the disk surface having excellent surface smoothness (for instance, surface roughness (Ra) and waviness (Wa)), having no surface defects such as projections, scratches, and pits, and being free from errors when reading-writing magnetic information caused by these surface defects.
Also, in the field of semiconductors, the trends of producing thinner wiring have been progressed along with the trends of highly integrated circuits and higher speed at the operating frequencies. Even in the process of producing a semiconductor device, since the focal depth becomes shallow with the trend of thinning the wiring during the exposure of a photoresist, further smoothening of a pattern-forming surface has been desired.
However, in the conventionally used abrasives produced by pulverization, since polishing damages are generated on the polished surface by the coarse grains remaining in the abrasive, there arises a defect that it has been difficult to carry out polishing, with maintaining a surface quality having the above-mentioned surface smoothness. For instance, there is disclosed a glass or silica polishing composition comprising an aqueous dispersion comprising fine serium oxide particles of which particle size distribution of the particle size has two main peaks (Japanese Patent Laid-Open No. 2000-38572). However, the resulting polishing rate and the quality of the polished surface are each unsatisfactory.
In view of the above, a colloidal silica having a narrow particle size distribution and little contamination of the coarse grains has been used. However, when polished with the colloidal silica, although it is relatively easy to accomplish a required high surface precision, there arise some defects that the polishing rate is delayed due to its fine particle size, so that a desired surface precision cannot be obtained in a short time period.
Therefore, as a process of improving the polishing rate, improvements in the polishing rate by using various additives in combination therewith have been proposed. However, none of them were sufficient for accomplishing satisfactory polishing rate. For instance, there is disclosed a polishing composition comprising water, colloidal particles (colloidal silica), aluminum nitrate and a gel-formation preventing agent (Japanese Patent Laid-Open No. Hei 9-204657), but the polishing rate of the resulting polishing composition is unsatisfactory.
In addition, when polishing with the above-mentioned colloidal silica, because of its small particle size, there also arises a defect that a colloidal silica deposited on the polished substrate in the cleaning step after polishing cannot be readily removed. The abrasive remaining on the polished substrate gives rise to causations of unevenness in the thickness of the magnetic recording layer, and the like, thereby resulting in the possibility that the magnetic properties are unstable. Moreover, when the magnetic properties are unstable, there undesirably arise causations for the generation of read-write errors.
In order to solve this defect, various cleaning process for completely removing the remaining abrasive in the cleaning process have been tried without yet achieving a satisfactory level. In addition, since the trend of making the abrasive finer is considered to further progress, its removal has become an increasingly important problem to be solved.
An object of the present invention is to provide a polishing composition which is used for finish-polishing memory hard disks and polishing semiconductor elements, in which the surface smoothness of a polished object after polishing is excellent, no surface defects such as projections and polishing damages are generated, and polishing can be carried out therewith at an economical rate; and a polishing composition capable of maintaining the surface smoothness of the polished substrate, having no surface defects generated, and polishing at an economical rate, without substantially allowing the abrasive to remain on the polished substrate in the cleaning step after polishing.
Another object of the present invention is to provide a polishing process of a substrate to be polished by applying the polishing composition, and a process for producing a substrate by applying the polishing composition.
These and other objects of the present invention will be apparent from the following description.
According to the present invention, there are provided:
[1] a polishing composition comprising an abrasive and water, wherein the abrasive has a particle size distribution such that (1) a ratio of D90 to D50 (D90/D50) is from 1.3 to 3.0, and (2) D50 is from 10 to 600 nm, wherein D90 is defined as a particle size at 90% counted from a smaller size side on a number base in a cumulative particle size distribution, and wherein D50 is defined as a particle size at 50% counted from a smaller size side on a number base in a cumulative particle size distribution;
[2] a polishing composition comprising two or more types of abrasives of which D50s are different from each other and water, wherein a ratio of D50L to D50S (D50L/D50S) is from 1.1 to 3.0, and a weight ratio of an abrasive (A) to an abrasive (B) [A/B] is from 90/10 to 10/90, wherein D50 is defined as a particle size at 50% counted from a smaller size side on a number base in a cumulative particle size distribution, wherein the abrasive (A) is defined as an abrasive having the smallest D50 and the abrasive (B) is defined as an abrasive having the largest D50, and wherein D50L is defined as a D50 owned by the abrasive (B) and D50S is defined as a D50 owned by the abrasive (A);
[3] a polishing composition comprising an abrasive and water, wherein the abrasive has a particle size distribution such that (3) a percentage at a particle size of 40 nm counted from a smaller size side on a number base in a cumulative particle size distribution is 25% or less, and wherein (4) D50 is from 50 to 600 nm, wherein D50 is defined as a particle size at 50% counted from a smaller size side on a number base in a cumulative particle size distribution;
[4] a polishing process of a substrate to be polished comprising polishing the substrate to be polished with the polishing composition of any of items [1] to [3] above; and
[5] a process for producing a substrate, comprising the step of polishing a substrate to be polished with the polishing composition of any of items [1] to [3] above.